The instant invention relates to systems and methods for controlling the actuation of vehicle safety devices and, more particularly, to systems and methods which utilize one or more evaluative measures with which to analyze events possibly requiring actuation of the safety device, wherein each measure is a function of received physical information such as transitory vehicle acceleration information and/or the transitory position of a passenger relative to a fixed structure within the vehicle, and wherein at least one of the measures is calculated by differentiating the received physical information or a function thereof with respect to time.
A variety of systems and methods for actuating vehicle safety devices are well known in the art. Such systems are used to sense an event such as a crash condition and, in response to such an event, to actuate an air bag, or lock a seat belt, or actuate a pretensioner for a seat belt retractor. Typically, the safety device is actuated into its protective position when an impact exceeding a predetermined magnitude is detected by the actuating system.
Significantly, known systems and methods for controlling actuation of vehicle safety devices typically rely on changes in one or more estimated physical quantities or crash-discrimination "measures" in determining whether to actuate the safety device. Oftentimes, one or more of these evaluative measures (or an intermediate measure useful in the determination of these measures) is obtained by differentiating received physical information, such as transitory vehicle acceleration information and/or the transitory position of a passenger relative to a fixed structure within the vehicle, with respect to time. One such known measure, a jerk value or "slope of acceleration" value, is obtained by differentiating received vehicle acceleration information over time. Another known measure, variance-itself a statistical measure of variation among a given number of sampled values--is obtained as by storing and rank-ordering received acceleration information so as to obtain a highest-ranked acceleration value within the stored sample and a lowest-ranked acceleration value within the sample, with the temporal variance value being the absolute value of the difference between the highest-ranked value and the lowest-ranked value.
Unfortunately, however, the use of differentiated information as when calculating jerk or variance values becomes problematic when transitory values for the information become negative, since a small positive value minus a large negative number generates an even larger positive value, which in turn tends to greatly distort any analysis based on that differentiated information. Indeed, where a waveform resonates about a small mean value, or even in the case of rough road inputs, an accumulated measure based on positive jerk or positive variance will quickly become meaningless, since its value will quickly surpass its triggering threshold to actuate the safety device irrespective of the true character of the event (whether a crash or an event not otherwise requiring actuation of the safety device).